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SOT: M42 Wiring for the 2002


ClayW

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With help from Jakeb, I created this diagram for anyone wishing to wire an M42 into their 2002.

M42WiringDone.jpg

Download the PDF below for decent resolution.

Enjoy.

EDIT: I will test this information out and make corrections. I'll post the corrected PDF in this thread.

M42 Wiring.pdf

ClayW
1967 1600-2 - M42 - 1521145          Follow my project at www.TX02.blogspot.com          E30 DD Project Blog

 

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i would be careful there.... the pinouts are pretty similar for all e30's. the s14/m3 install is well documented.

i would recommend using all the m42 wiring harness that applies rather than stringing 02 wires all over the engine. this includes the C101 connector. makes wiring cleaner and engine install/removal simpler.

the below specifics could be wrong as i am writing from memory...

pin 1 - not used? really? that is the alt d+ and should be connected to the blue 2002 alt wire to dash for alt and dash light to work

pin 4 - use it. sure, sub in 02 sensor in m42 location, but use the harness run and connect to the 02 wiring at firewall.

pin 6/7 - relay not needed. iirc they are just the signal wires to the engine harness main and evap relays, and the coil power which the o2 wire already handles. very little load here.

pin 13 - harness already has relay for fuel pump, but does not have fuse. need to put fuse on this output to pump(s).

diag plug - recommend using. think pin 16 is the starter trip connection.

2xM3

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i would be careful there.... the pinouts are pretty similar for all e30's. the s14/m3 install is well documented.

i would recommend using all the m42 wiring harness that applies rather than stringing 02 wires all over the engine. this includes the C101 connector. makes wiring cleaner and engine install/removal simpler.

the below specifics could be wrong as i am writing from memory...

pin 1 - not used? really? that is the alt d+ and should be connected to the blue 2002 alt wire to dash for alt and dash light to work

pin 4 - use it. sure, sub in 02 sensor in m42 location, but use the harness run and connect to the 02 wiring at firewall.

pin 6/7 - relay not needed. iirc they are just the signal wires to the engine harness main and evap relays, and the coil power which the o2 wire already handles. very little load here.

pin 13 - harness already has relay for fuel pump, but does not have fuse. need to put fuse on this output to pump(s).

diag plug - recommend using. think pin 16 is the starter trip connection.

This diagram is for using the C101 connection to the engine harness with a good pigtail on the chassis side. I wouldn't pass up using the M42 harness; it's too nice not to use!

You're right about the 1 Pin and the fuses. I'll test and correct the diagram when I wire everything up.

I'm not sure about pin 16, though. How would I use it?

ClayW
1967 1600-2 - M42 - 1521145          Follow my project at www.TX02.blogspot.com          E30 DD Project Blog

 

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This is how I have my M42 wired up and it works very well. I do have the alternator charge control hooked up as well and am currently turning the left portion of the fasten seatbelt sign into my check engine light. You may want to eliminate the extra harness for the Air Flow Meter. I believe it was only added to US cars for emissions reasons. My car runs a million times better without this.

Does anyone know if our cars came with the CO potentiometer? I believe it is in the Air Flow meter. You will notice a single wire connector thats disconnected with each end taped to the back of the engine harness. If you connect these wires it activates the CO potentiometer and is meant to decrease emissions in cars without catalytic converters. I am not sure if this is an extra sensor that is in the AFM or if it just uses the AFM signals to estimate the CO output. let me know.

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it the extra harness you are refering to the evap valve (not the af meter)? you kinda gotta have the afm in the system or the ecu does not know how much air is going in the engine. unless you are using AN for fuel management.

you can however, strip out the evap circuit, relay and wiring.

here is the ecu and c101 pinout diag.

connectin pin 16 allows you to run the starter from the diag plug, bypassing the ignition key.

post-18347-1366764098452_thumb.jpg

2xM3

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it the extra harness you are refering to the evap valve (not the af meter)? you kinda gotta have the afm in the system or the ecu does not know how much air is going in the engine. unless you are using AN for fuel management.

you can however, strip out the evap circuit, relay and wiring.

here is the ecu and c101 pinout diag.

connectin pin 16 allows you to run the starter from the diag plug, bypassing the ignition key.

I am refering to the extension harness added in series to the AFM wiring. It is about a foot long and hooks up directly to the AFM and the original AFM Connector. I believe it has a resistor to alter the signal from the AFM.

Also I am having trouble with my Check Engine Light. Pin 12 is not being grounded when it should be to turn on the SES light. any ideas?

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s14's have a barometric pressure sensor on same harness as the afm. small black box. engine will run without it, but will not compensate for air pressure changes. could that be what you are seeing?

don't know about your CEL issue. did it work before? i have not trace that system to see if ecu grounds or powers the CEL.

2xM3

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The ECU/DME grounds pin 12 when it wants to turn on the CEL. You have the other connection on the light connected to 12v. If your light is not turning on disconnect the wire from pin 12 that goes to the light and ground it with the key on to make sure the light works. If it does you might want to check continuity back to the DME. Or use a meter and see if the DME is grounding pin 12 when the key is on and dme is plugged in.

I have seen those little harnesses between the main m42 harness and the AFM once and awhile. I THINK it is something used if the AFM was replaced. Put a ohm meter and see if it is straight through or not.

1985 e28 w/LS1/t56 and a bit more...

1970 2002 w/ m42 swap

-Contact me for m42 mounts or e28 ls1 mounts-

www.classicdaily.net

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The ECU/DME grounds pin 12 when it wants to turn on the CEL. You have the other connection on the light connected to 12v. If your light is not turning on disconnect the wire from pin 12 that goes to the light and ground it with the key on to make sure the light works. If it does you might want to check continuity back to the DME. Or use a meter and see if the DME is grounding pin 12 when the key is on and dme is plugged in.

I have seen those little harnesses between the main m42 harness and the AFM once and awhile. I THINK it is something used if the AFM was replaced. Put a ohm meter and see if it is straight through or not.

I don't have the light hooked up yet for the CEL. I am just turning the Key to the Run position and using my multimeter on OHM setting with one side grounded and the other hooked up to the Wire coming out of pin 12. I have also checked continuity between the brown wire on the Engine side of the c101 and the brown/black wire that is on the chassis side of the C101 and they are definitely connected. I have a weird chassis c101 I bought off r3v I am not sure what it came out of but it has some odd wire colors, dont match up with any schematics I have so I have gone through and checked continuity on all the pins.

As for the added harness it does contain a little black box that all the wires go through and it does alter the signal to the DME. There must be resistors in the black box for some reason. As far as I can tell It is OEM AFM the plug hasn't even been pulled out to get to the adjustment screw (thank goodness!) I hate when people mess with these.

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I don't have the light hooked up yet for the CEL. I am just turning the Key to the Run position and using my multimeter on OHM setting with one side grounded and the other hooked up to the Wire coming out of pin 12. I have also checked continuity between the brown wire on the Engine side of the c101 and the brown/black wire that is on the chassis side of the C101 and they are definitely connected. I have a weird chassis c101 I bought off r3v I am not sure what it came out of but it has some odd wire colors, dont match up with any schematics I have so I have gone through and checked continuity on all the pins.

As for the added harness it does contain a little black box that all the wires go through and it does alter the signal to the DME. There must be resistors in the black box for some reason. As far as I can tell It is OEM AFM the plug hasn't even been pulled out to get to the adjustment screw (thank goodness!) I hate when people mess with these.

And when in the run position you still show an open connection at pin 12 on the meter? I would try hooking up a light and see what you get.

1985 e28 w/LS1/t56 and a bit more...

1970 2002 w/ m42 swap

-Contact me for m42 mounts or e28 ls1 mounts-

www.classicdaily.net

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